The main frequency and frequency stability determining element in crystal oscillators is the crystal resonator. The resonance frequencies of crystal resonators change with temperature. Therefore, in the highest stability crystal oscillators, the resonator's temperature is kept constant in an oven. The main drawback of such oven controlled crystal oscillators (OCXO) is the power requirement, that usually prevents the use of OCXOs in battery operated equipment. Designers of OCXOs have strived to minimize the power requirements by using low thermal conductivity materials, such as foam insulators, to isolate the oven from the environment.
The best thermal insulator is a vacuum, together with appropriately finished surfaces in the oven to minimize heat losses by means of radiation. The "tactical miniature crystal oscillator" (TMXO), for example, uses vacuum for thermal insulation, however, using vacuum alone results in some undesirable side effects. The two major side effects are resonances in the mounting structure and manufacturing costs.
Supporting the oscillator in a vacuum insulated enclosure requires some difficult tradeoffs between minimizing heat losses through the supporting structure and providing a sufficiently rigid structure for the vibration resonances to be inconsequential. Wires and thin-walled tubes have been used in the TMXO in attempts to strike a proper balance between the conflicting requirements. The attempts have been only partially successful.
The acceleration sensitivity of crystal oscillators is troublesome in many applications, e.g., in radar systems, especially when the system must operate from a vibrating platform such as an aircraft. Even the lowest acceleration sensitivity oscillators are inadequate in some advanced radar applications, for example. When the oscillator's supporting structure results in resonances at the frequencies that affect the system's performance, the adverse effects of the oscillator's acceleration sensitivity are magnified. In applications where the oscillator's acceleration sensitivity is excessive, vibration isolation is usually employed. The isolation systems present problems of their own, i.e. added size, weight and cost, poor performance against acoustic noise induced vibration, and resonances of the isolation system. Above the isolation system's resonance frequency, the isolation system can be effective, however, at and below that frequency, the isolation system magnifies the problems.
Thus, there exists a need for a low cost, easily manufactured manner in which to isolate an oscillator. The present invention addresses such a need.